1. Field of the Invention
The present invention relates to a wafer retaining mechanism, in particular to one including more than one link unit each of which has a sliding link, a lower link, a front link, an upper link, and associated pins, thereby the link units can urge, and retain securely, the wafers contained in a wafer cassette.
2. Description of the Prior Art
Conventionally various devices are provided for preventing the semiconductor wafers from being jarred or bumped when the wafers are transported or stored. Especially, particulate release may be caused when jarring occurs resulting in abrasion between the wafers and the contacted surfaces of a wafer cassette. To prevent wafer damage and particulate release, the wafers must be held securely within the wafer cassette.
U.S. Pat. No. 5,452,795 issued to Gallagher et al. relates to an actuated rotary retainer for silicone wafer box. The rotary retainer is attached to the sidewall of a box to prevent movement of the wafers within a wafer cassette during transportation and storage. The rotary retainer consists of an elongated shaft, fingers, a coil spring, a first bearing, and a second bearing. The first and second bearings are attached to the box, and the elongated shaft is rotably coupled to the bores of the first and second bearings. The shaft is coupled to the first and second bearings, wherein the shaft bottom contacts a door as the box and the door are engaged. The shaft rotates through the bore from a first position to a second position when the box and the door are engaged. The first and second bearings are attached to the box inner sidewall, whereby a peg of the shaft first comes into slight contact with the bottom and of a sloped rotation member when the box and door are fully engaged. The fingers retain the semiconductor wafers within the semiconductor wafer cassette when the box is engaged with the door. The wafer retaining fingers are positioned on the shaft, whereby, when the box and door are engaged, the fingers align with wafers stored in individual slots of the wafer cassette. The wafer retaining fingers absorb force from the wafers when the box is jarred during transportation.
Further, U.S. Pat. No. 4,815,912 issued to Maney et al. relates to a box door actuated retainer comprising a tongue, a box door member which extends along with the length of the tongue, a first parallelogram arm attached to the door member, two side arms attached to a box at two display locations which form a second parallelogram arm. The first and second arms are the same length as are the side arms. The side arms are pivotively connected to the first and second arms. When the box door is opened and lowered, the box door member is also lowered by the operation of gravity, causing the side arms to pivot. The pivoting of the side arms causes the tongue to travel not only downward, but also retracting away from the wafers contained in a cassette. As such, the cassette and the wafers are enabled to be easily withdrawn out of the box. When the cassette and the wafers are to be returned back into the box, the box door contacts the bottom of the box door member (though until the box door contacts the bottom position of the box door member, the retainer remains away from the wafers), the tongue moves toward and abutting upon the wafers contained in the cassette. Therefore, even if the box may be jarred or bumped, the wafers are restrained from any substantial movement. This restraint tends to reduce the movement of contamination particles.
The present invention is intended to provide a wafer retaining mechanism having a structure quite different from that disclosed in the '795 patent, while somewhat similar to that disclosed in the '912 patent in the sense that a linkage is used, the present invention serves to improve the effect in retaining the wafers contained in a cassette.